This invention is generally directed to imaging members and their utilization in, for example, electrophotography, and more specifically, to photogenerating layers comprised of photogenerating pigments dispersed in a mixture of polymeric binders to thereby enable, for example, improved photosensitivity thereof and other advantages as illustrated herein. The resulting layered imaging members possess a number of advantages, such as high photoconductivity, low dark decay and excellent stability over extended xerographic cycling, for example from about 1 percent to about 20 percent cycle down after 50,000 imaging cycles, flat spectral response at 400 to 900 nanometers in embodiments, and wherein, for example, the imaging members with photogenerating pigments like benzimidazole perylene have improved photosensitivity of E.sub.1/2 of 3 ergs/cm.sup.2 as compared to an E.sub.1/2 of greater than 4 ergs/cm.sup.2 for similar imaging members with a single binder for the photogenerating pigments.
Generally, layered photoresponsive imaging members are described in a number of U.S. patents, such as U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference, wherein there is illustrated an imaging member comprised of a photogenerating layer, and an aryl amine hole transport layer. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, oxymetallo phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating polymeric binder. The binder materials disclosed in the '006 patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Polymeric binders for the photogenerating pigments include, for example, polycarbonates, polyvinylcarbazole, and the like. Also, illustrative examples of polymeric binder resinous materials that can be selected for the photogenerator pigment include those polymers as disclosed in U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference.
In a copending application U.S. Ser. No. 537,714, the disclosure of which is totally incorporated herein by reference, there are illustrated photoresponsive imaging members with photogenerating oxytitanium phthalocyanine layers prepared by vacuum deposition dispersed in for example certain single resin binders like polycarbonates. It is indicated in this copending application that the imaging members comprised of the vacuum deposited oxytitanium phthalocyanines and aryl amine hole transporting compounds exhibit superior xerographic performance, since low dark decay characteristics result and higher photosensitivity is observed, particularly in comparison to several prior art imaging members prepared by solution coating or spray coating, reference, for example, U.S. Pat. No. 4,429,029.
In U.S. Pat. No. 5,206,359 there are disclosed imaging members with titanyl phthalocyanine photogenerating pigments dispersed in, for example, certain single resin binders, and wherein the phthalocyanine is prepared by the treatment of Type X oxytitanium phthalocyanine with a halobenzene; and more specifically, the solubilization of a Type I oxytitanium phthalocyanine, which can be obtained by the reaction of 1,3-diiminoisoindoline and titanium tetrabutoxide in the presence of a solvent, such as chloronaphthalene, reference U.S. Pat. No. 5,189,156, the disclosure of which is totally incorporated herein by reference, in a mixture of trifluoroacetic acid and methylene chloride, precipitation of the desired Type X oxytitanium phthalocyanine, separation by, for example, filtration, and thereafter subjecting the product to washing with fluorobenzene.
Perylene pigments, particularly the derivatives thereof prepared from perylene-3,4,9,10-tetracarboxylic acids or anhydrides, are useful photogenerating materials in layered imaging members for electrophotographic applications. For example, U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, illustrates imaging members containing a benzimidazole perylene layer prepared by vacuum evaporation or dispersion in a single polymeric binder. Other photogenerating pigments, such as azos, phthalocyanines, polycyclic quinones, squaraines, and the like, have been used in imaging members fabricated by vacuum evaporation, binder solution coatings or binderless pigment dispersions.
Also of interest is U.S. Pat. No. 4,514,482, the disclosure of which is totally incorporated herein by reference, directed to perylene photoconductive devices.
Improvement in the photosensitivity of photoconducting imaging members would have several advantages in the operation of electrophotography printing processes, for example the printing speed can be improved resulting in higher productivity. The required power of illuminating sources such as lasers, light emitting diodes, liquid crystal imaging bars, electric lamps, used to create the latent images on the photoconducting imaging member can be significantly reduced leading to cost savings in the hardware and operation aspects. Thus, the efficiency of imaging members can be increased when there is improvement in the photosensitivity thereof. Therefore, it is evident there is continued desire to improve the photoresponse properties of imaging members.
This invention in embodiments primarily relates to imaging members comprised of photogenerating pigments, like benzimidazole perylene prepared with selected mixtures of polymeric binders, which exhibit an unexpected improvement in photosensitivity as compared to, for example, when only a single binder was employed in preparing the imaging members. In addition, the mixed binders also possess additional advantages over the single binder system such as improvements in mechanical properties, superior pigment dispersion, and the like. The ability of maintaining mechanical integrity in layered imaging members is important as the delamination or large dimensional distortion of its various layers would be lead to severe degradation of image quality or complete operational failure. The pigment dispersion quality of the imaging members can have a strong impact on its printing quality such as graininess, resolution, uniformity of solid areas and the like, advantages achievable with the present invention in embodiments.
It is an objective of this invention to provide significant improvements in photosensitivity and other properties such as mechanical, and printing quality of the imaging members formed by using a mixture of binders instead of a single binder in dispersing the photogenerating pigments, and processes thereof.